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Convergence of series, sequences and functions and different modes of convergence.

1 vote
Accepted

How to prove this iterative convergence of trigonometric functions

Let's use induction on all sequences of length $n$. For length $1$ we have $2\sin(\frac{\pi}4 s_0) = s_0$, but actually $2\sin(\frac{\pi}4 s_0) = s_0 \sqrt 2$, so there's a slight error in the questio …
Daniel Weber's user avatar
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7 votes

$\lim_{n \to \infty} \frac{2^n}{n} \left[ 1 - \sum_{k = 1}^{n-1} \frac{(1 - \lambda 2^{-n})^...

We have $$(1 - \lambda 2^{-n})^{2^k} = e ^ {2^k \log(1 - \lambda 2^{-n})} = e ^ {2^k ( - \lambda 2^{-n} + O_\lambda(4^{-n}))} = e^{-\lambda 2^{k-n} + O_\lambda(2^{-n})} = (1 + O_\lambda(2^{-n})) e^{-\ …
Daniel Weber's user avatar
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46 votes
Accepted

A challenging (for me) limit calculation

This limit converges to $\frac{\sqrt3}2$. The idea is that $\sin(x) = x - \frac{x^3}6 + O(x^5)$, so we start with $\frac1{\sqrt n}$ and repeatedly subtract $\frac{x^3}6$. We can approximate this discr …
Daniel Weber's user avatar
  • 3,319